Autologous transplantation of myoblast sheet has attracted attention as a new technique for curing myocardial infarction. Myoblast sheet has the ability to secret cytokines that improve heart function via the facilitation of angiogenesis on affected part. To mimic the in vivo angiogenesis in the myoblast sheet after transplantation, a five-layered cell sheet of human skeletal muscle myoblasts (HSMMs) was overlaid on human umbilical vein endothelial cells (HUVECs) which enables evaluation of dynamic HUVEC behavior. HUVECs existing initially at the bottom of the sheet changed to be a stretched shape and migrated upward compared with the surrounding HSMMs in the sheet. Prolonged incubation resulted in network formation of HUVECs in the middle of the sheet, although non-networked HUVECs continued to migrate to the top of the sheet, which meant the spatial habitation of HUVECs in the cell sheet. Image processing was performed to determine the variation in the extent of network formation at different HUVEC densities. It was found that the extent of formed network depended on the frequency of encounters among HUVECs in the middle of the sheet. The present system, which can evaluate network formation, is considered to be a promising in vitro angiogenesis model.